The present invention relates to a novel ultimate analyzer for analyzing elements of an object to be analyzed based on an output signal of a scattered electron beam and a plurality of output signals of an electron beam energy dispersed after passing through an object to be analyzed, and a scanning transmission electron microscope having the ultimate analyzer and an ultimate analysis method using the scanning transmission electron microscope.
With progressing of miniaturizing and downsizing of semiconductor devices and magnetic head elements, the structure of these elements has a structure that thin films of several nm (nanometers) are laminated in an area of a sub-micrometer order. Since the characteristics of the semiconductor elements and the magnetic head elements strongly depend on the structure, the element distribution and the crystal structure in such a micro-area, it is important to analyze them in the micro-area.
As the means for observing a micro-area, there are a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a scanning transmission electron microscope (STEM). Only the TEM and the STEM have a spatial resolution of a nanometer level. The TEM is an apparatus in which an electron beam is irradiated onto a sample, and the transmitted electron beam is magnified using a lens. On the other hand, the STEM is an apparatus in which an electron beam is focused onto a micro-area, and a two-dimensional image is obtained by measuring intensities of the transmitted electron beam while the electron beam is being scanned on the sample.
As the means for observing a two-dimensional distribution of elements on a plane of a sample, there are an energy dispersive X-ray spectroscopy (EDX) and an electron energy loss spectroscopy (EELS) using the TEM or the STEM. For example, in a case of analyzing a metal film, Cr, Mn, Fe, Co, Ni and Cu can be identified using the energy dispersive X-ray spectroscopy, and two-dimensional distributions of the above metals can be obtained.
On the other hand, by using the electron energy loss spectroscopy, silicon, oxygen and nitrogen can be identified, and two-dimensional distributions of silicon, silicon oxide and silicon nitride can be observed. The electron energy loss spectroscopy is a method of analyzing lost energy for exciting inner-shell electrons of elements composing a sample when the electron beam transmitting through the sample. The electron that lost energy due to the excitation of the inner-shell of the element to be analyzed is called as core-loss electron. The ultimate analysis can be performed because the lost energy is specific to an element, and a two-dimensional distribution of the elements can be observed by performing energy analysis in each position in the plane of the sample. These spectroscopy are widely used by combining the STEM and a parallel detection type electron beam energy loss spectrometer.
The parallel detection type electron beam energy loss spectrometer comprises a magnetic-prism spectrometer; quadrupole electromagnetic lenses and hexapole electromagnetic lenses arranged at the front of and at the rear of the magnetic-prism spectrometer; and a parallel detector arranged after the magnetic-prism spectrometer. The quadrupole electromagnetic lenses are used for adjusting focus of the electron energy loss spectra and for magnifying the electron energy loss spectra. The hexapole electromagnetic lens is used for reducing aberration of the electron energy loss spectra projected on the detector. The electron energy loss spectra magnified by the quadrupole electromagnetic lens is projected on the parallel detector to measure a wide range of the electron energy loss spectra.
The prior art in regard to the structure of the parallel detection type electron energy loss spectrometer is disclosed in, for example, U.S. Pat. No. 4,743,756, Japanese Patent Application Laid-Open No. 7-21966, Japanese Patent Application Laid-Open No. 7-21967, and Japanese Patent Application Laid-Open No. 7-29544. An electron energy analyzer is disclosed in Japanese Patent Application Laid-Open No. 57-80649.
In a conventional apparatus combining the parallel detection type electron energy loss spectrometer and the STEM, a user performs (1) specifying a measured position, (2) specifying an element, (3) measuring an energy intensity distribution of the electron beam using the electron beam detection part, (4) correcting background of the detection part and correcting the gain of the detection part, (5) specifying a background region of the spectrum, (6) specifying a background fitting function such as the power-low model (I=Axc3x97Exe2x88x921; A and r are coefficients, and E is energy), (7) specifying an integration region of the signal intensity, (8) displaying the signal intensity of the specified element in the measured position on the image display unit, and (9) performing the operation of the item (1). Since it is necessary to perform the repetitive operation described above for all the measuring points, it takes a long time to obtain a two-dimensional image, and accordingly it is difficult to obtain an element distribution in real time. Further, it can be considered to obtain the two-dimensional image by the method that after measuring the electron energy loss spectra for all the measured points, the user specifies the operations of (2) to (7). In this method, the volume of measured data becomes very large, and further, the element distribution image can not be obtained in real time.
In addition to the above, in the case where the element distribution image can not be obtained in real time, there are following problems:
(A) In a case where analysis of an interface between thin films, the analysis region (the interface between thin films) can not be identified by using a TEM/STEM image when measuring the electron energy loss spectra. Accordingly, whether or not the region to be measured is included in the analyzed region cannot be judged until the element distribution image is obtained after analyzing the electron energy loss spectra.
(B) The conventional analyzer is not suitable for the work such as the inspection to measure many samples because it requires the measurement of the electron energy loss spectra and the many complicated and complex operations for each measured point, and also it requires a long time for the measurement and the analysis.
(C) In a case of identifying an oxide film or a deposited element formed in an interface between dissimilar metals, it cannot be identified by observing only a distribution image of the single element which metal between the dissimilar metals is oxidized, or it is difficult to be identified by observing the element distribution image whether the elements exist on the interface between the dissimilar metals or are distributed inside one of the metals.
Further, in an analyzer which detects an element to be analyzed by dividing an intensity of a first electron beam in an energy range containing a core-loss peak among the electron energy loss spectra of the element to be measured by an intensity of a second electron beam in an energy range higher than the core-loss peak, which is called as a jump-ratio method, there is the following problem depending on the sample to be analyzed.
When light elements such as oxygen, nitrogen and the like are observed in a case where a heavy metal element exists in the sample to be measured, a portion of the heavy metal element is sometimes displayed with brightness similar to brightness of the distribution image of the light elements. In that case, since the contrast difference between a metal portion and an oxide or nitride portion becomes small, it becomes difficult to judge correctly existence of oxide or nitride.
As described above, the analyzer combining the electron energy loss spectrometer and the STEM is difficult to observe an element distribution image having high contrast in real time and to determine the distribution of the element with high accuracy.
On the other hand, as a means for preventing degradation of an image due to brightness variation of an electron source in STEM image observation using a scanning transmission electron microscope, Japanese Patent Application Laid-Open No. 2000-21346 discloses a scanning transmission electron microscope in which one of an output signal from a detecting means for detecting transmission electrons transmitted through a sample and an output signal from a detecting means for detecting scattered electrons scattered by the sample is divided by the other. However, this patent discloses a means for improving image quality of a STEM image, but not a means for analyzing elements of the sample.
The literature by K. Kaji, et al., xe2x80x9cLight Element Mapping Method with Scanning Transmission Electron Microscopexe2x80x9d, The Japanese Society of Electron Microscopy, May 17, 2000: p307, describes a method for obtaining an oxygen distribution image, in which gate electrodes are dark and oxidized films thereon are bright.
According to the description, using a transmission electron scanning microscope of a field-emission type and an ultimate analyzing observation apparatus, the method obtains such image by logical dividing operation applied to an oxygen distribution image acquired by 2-window method using a Z-contrast image as the divisor.
However, this method is still not enough to respond to the demand for more contrasted screen-displaying of gate electrodes and oxidized films thereon.
An object of the present invention is to provide an ultimate analyzer which can display an element distribution image of an object to be analyzed with high contrast to determine the positions of the element distribution with high accuracy, and a scanning transmission electron microscope and a method of analyzing elements using the ultimate analyzer.
The present invention is characterized by an ultimate analyzer comprising a control unit for detecting an element of an object to be analyzed based on an output signal of an electron beam detector by dispersing an electron beam transmitted through a sample, particularly, based on an intensity of the output signal and an output signal of a ring-shaped scatted electron beam detector for detecting an electron beam scattered by the sample.
Further, the present invention is characterized by an ultimate analyzer comprising an image display unit for displaying an element distribution image of an object to be analyzed obtained based on an intensity of an electron beam detected by an electron detector passing through a sample and being dispersed; and an element distribution image of the object to be analyzed obtained based on an intensity of an electron beam detected by the scattered electron beam detector described above.
Further, the present invention is characterized by an ultimate analyzer comprising any one of an image display unit for displaying line profiles of an element of the object to be analyzed obtained from an analysis result output from a control unit for analyzing the element of the object to be analyzed based on an intensity of the dispersed electron beam detected by the electron beam detector and an analysis result output from the control unit for analyzing the element of the object to be analyzed based on an intensity of the electron beam detected by the scattered electron beam detector, and an image display for displaying a distribution image of the element, and an image display unit for displaying the distribution image of the element and a distribution image of the element based on the intensity of the electron beam detected by the scattered electron beam detector with two image planes side-by-side at a time or with sequential one-image planes or with two image planes overlapped with each other. The output signal detected by the electron beam detector is expressed by the intensity, but the electron beam detector detects an amount of electrons.
Further, the present invention is characterized by a scanning transmission electron microscope comprising an electron beam source for generating an electron beam; an electron beam scanning coil; a scattered electron beam detector for detecting a scattered electron beam scattered by an object to be analyzed; an objective lens for condensing the electron beam on the object to be analyzed; a focusing lens; a magnifying magnetic field lens; a focus adjusting electromagnetic lens; a scanning portion for scanning the electron beam; an electron dispersing portion for energy-dispersing the electron beam; and an electron beam detector portion for detecting part or all of the electron beam energy-dispersed by the electron dispersing portion, which comprises the ultimate analyzer described above.
That is, the present invention is characterized by a scanning transmission electron microscope comprising a processor for performing operation using only an intensity of an electron beam detected by the electron beam detector for detecting at least part of the electron beam dispersed by the electron dispersing portion or using both of the intensity of the electron beam and a result of an intensity of an electron beam detected by the scattered electron beam detector, and displays the operated result of the processor at the same time or in parallel with scanning the electron beam using the scanning portion or after the electron beam scanning. Further, the present invention is characterized by that an image based on the electron beam intensity detected by the scattered electron beam detecting portion is displayed together with the operated result of the processor side-by-side or overlapping with each other. Therefore, by the analyzer combining an electron energy loss spectrometer and an STEM, an element distribution image can be displayed on a screen in real time.
Further, the present invention is characterized by a scanning transmission electron microscope comprising the dispersing conditions of the electron beam losing energy due to the excitation of the inner-shell electron in the element to be analyzed; and two or more channels of electron beam detecting portions for detecting dispersed electron beams, wherein the ultimate analysis is progressed by specifying a element to be observed after specifying a measurement region; then obtaining energy dispersing conditions of core-loss electrons of the specified element from a dispersing condition memory unit; automatically adjusting the electron optical system of the electron dispersing portion and the electron beam detecting portion so that the core-loss electrons may be detected; measuring an intensity of the core-loss electrons and an intensity of electrons just lower than the energy of core-loss electrons by the electron beam detecting portion using at least one channel for each while the electron beam is being scanned using the scanning portion; performing background correction and gain correction of the electron beam detecting portion using the processor; executing operation, preferably, dividing an intensity of an electron beam of the core-loss edge in an electron energy loss spectrum by the intensity of an electron beam just before the core-loss edge; and displaying both of the operated result obtained by the division and the result based on the intensity of the electron beam detected by the scattered electron beam detector on the image display unit at a time or in parallel or overlapped with each other in real time.
Further, the scanning transmission electron microscope in accordance with the present invention is characterized by that the operated result obtained by dividing the intensity of an electron beam including core-loss electrons by the intensity of an electron beam whose energy is smaller than the energy of core-loss electrons is operated using the intensity of the electron beam detected by the scattered electron beam detecting portion, and the operated result obtained as the result is displayed solely or together with side-by-side or overlapped with an image based on the intensity of the electron beam detected by the scattered electron beam detecting portion on the image display unit in real time. When an image is formed by electrons scattered by a sample in a high angle using the scattered electron beam detecting portion, the obtained image is also called as a Z-contrast image.
The present invention is characterized by an ultimate analyzer which can observe and display an element distribution image and a Z-contrast image at a time in real time during scanning the electron beam, and can observe an element distribution image corrected by the Z-contrast image.
The present invention is characterized by an ultimate analysis method comprising the steps of detecting an output signal of an electron beam penetrated through an object to be analyzed, preferably as an intensity for each energy of the electron beam; and analyzing an element, preferably a non-metallic element, of the object to be analyzed based on an output signal of the detected electron beam, wherein the intensity of the output signal is corrected by an output signal, preferably by an intensity, of the electron beam scattered by the object to be analyzed.
Further, the present invention is characterized by that in the electron energy loss spectrum obtained by dispersing energy of an electron beam penetrated through an object to be analyzed, analysis of element of the object to be analyzed obtained by operating based on both an intensity of an electron beam within an energy range including a core-loss edge appearing in the electron energy loss spectrum by electrons exciting the inner-shell electron of an element composing the object to be analyzed and an intensity of an electron beam having a higher energy than the core-loss edge or the element analysis image are obtained by correcting the intensity of the electron beam scattered by the object to be analyzed.
Further, the present invention is characterized by that in an ultimate analysis method comprising the steps of detecting an intensity of an electron beam penetrated through an object to be analyzed; analyzing an element of the object to be analyzed based on the intensity and loss-energy of the detected electron beam; and displaying an image of the ultimate analysis on a screen, wherein the image of the ultimate analysis is displayed on the screen by being corrected by a Z-contrast image obtained from operation based on an intensity of an electron beam scattered by the object to be analyzed.
The present invention is to provide an ultimate analyzer comprising: a control unit for analyzing elements of said object to be analyzed based on a computed output signal obtained either through adding or subtracting operation applied between an intensity of a transmitted electron beam and an intensity of a scattered electron beam or through dividing operation applied to said transmitted beam intensity using the square root of said scattered beam intensity as the divisor; and a computing unit either for adding or subtracting operation between the intensity of said transmission electron beam and the intensity of said scattered electron beam or for dividing operation to said transmission beam intensity using the square root of said scattered electron beam intensity as the divisor; and a screen-display device for the corrected image of the analyzed results.
Another feature of the present invention is to provide a method for ultimate analysis comprising the steps of: correcting an image based on a computed output signal obtained either through adding or subtracting operation applied between an intensity of a transmitted electron beam and an intensity of a scattered electron beam or through dividing operation applied to said transmitted beam intensity using the square root of said scattered beam intensity as the divisor; and displaying the corrected image on a screen.
Said ultimate analysis image and a Z-contrast image may be displayed in any of styles: a side-by-side shared-screen assignment for said analysis image and said Z-contrast image, another side-by-side shared-screen assignment for said Z-contrast image and a processed image obtained by logically dividing said analysis image by said Z-contrast image, a switching display wherein said analysis image or said Z-contrast image appears by switching, or superimposed display of said ultimate analysis image and said Z-contrast image each being given contrast gradation with colors other than black and white but different each other.
On every electron beam position irradiated onto a specimen, the ultimate analysis result obtained through EELS spectrum or the same but obtained through EELS spectrum and said Z-contrast image is displayed. This means that the line profile is displayed.